Hi Destiny
There are many things that can cause that kind of noise. You are likely on the right track with the belt tensioner pulley, however it may be one of the other pulleys, or a problem with the tensioner itself. A belt that is too tight can also cause that, I've seen it where an incorect belt was installed and it fits, but just barely and because its too tight it never quiets down.
You might also try remove the belt completely and run the engine to make sure the noise goes away. This will tel you if it is something run by the belt or if it is something else entirely. Be careful though, you only run the engine for a few minutes like this, the battery will die and the car will overheat if you run it for too long.
But you should be able to tell in just a few moments if its still there or not.
Once you've determined if it is in fact belt reled, spin each of the pulley to see if one of them is bad (feels/sounds rough while spinning by hand).
Hope that helps! If all else fails, take it to a certified shop and have them figure it out.
Bogi Lateiner
180 Degrees Automotive
http:/www.180auto.com/

If the tensioner pulley and belt were replaced, you may have a bad bearing in an idler pulley or possibly the alternator or air conditioning compressor. With the engine running, attempt to determine where the squeal is coming from. Always use caution when under the hood of a running vehicle, avoiding rotating parts and the drive belt. Hope this helps. Super Girls Auto